1. Field of the Invention
This invention relates generally to object-oriented sonar system simulators and more particularly to an object-oriented system for simulating bistatic sonar target acoustic scattering behavior.
2. Description of the Related Art
Active and passive sonar systems are well-known. An active sonar system generally includes a transmitter and acoustic transducer that produces an acoustic source signal, creating a scattering and propagating wave front. A receiving transducer array detects a received acoustic signal representing the incidence of a reflected portion of the source signal wave front. Passive sonar systems consist substantially of the receiving transducer array and the target object becomes the transmitter of the acoustic source signal in the form of noise from the target object or transmissions from other active sonar devices.
Accurate target models capable of predicting the echo time history of submarines and surface ships are essential tools for antisubmarine warfare and ship vulnerability studies. A realistic model must account for the many highlights of a target, the conditions of insonification, and the proper highlight amplitude and phase to predict temporal and spectral behavior. The physical scattering mechanisms must be properly identified and incorporated into the model.
Over the past thirty years, practitioners in the sonar system arts have steadily improved the Uniform Theory of Diffraction (UTD) target model, which have proven to be an invaluable asset for the development of torpedo and surveillance systems signal processing algorithms and simulations. Previous formulations of the UTD target models, dictated by the computational limitations of past simulation systems have been limited to monostatic and far-field configurations for narrowband applications. They also were limited to a simple Doppler implementation. These restrictions simplified the numerical implementation (and theoretical development) considerably and they serve well in deep-water and other benign environments. However, in the littoral environment now paramount in the military and geopolitical milieu, more sophistication is required.
Numerous practitioners have proposed improvement to the sonar modeling art intended to accommodate the special problems of the littoral environment. For instance, in U.S. Pat. No. 5,983,067, Weinberg discloses a system for simulating the features of a multipath sonar system, such as reverberation, lofargrams, autocorrelation coefficients and cross-correlation coefficients in a littoral environment. However, Weinberg relies on eigenray simulation and neither considers nor suggests means for accommodating the computational complexity of a detailed sonar target scattering model.
The strong need in the art for improved broadband modeling has prompted the development of broadband target models of high fidelity. See, for instance G. A. Lengua, xe2x80x9cFrequency Dependencies of Target Highlights,xe2x80x9d NRaD Technical Report 1752, Naval Command, Control, and Ocean Surveillance Center, San Diego, Calif., August 1997. These have served as invaluable simulation tools. However, the significant multipath structure of littoral environments requires bistatic target models of high fidelity, which impose major computational burdens on existing simulation systems. Practical considerations demand computational efficiency but existing simulation techniques are not robust enough to handle the complexity arising from including bistatic response of target highlights with sophisticated Doppler and broadband implementation.
These unresolved problems and deficiencies are clearly felt in the art and are solved by this invention in the manner described below.
This invention resolves the above-described detailed sonar target scattering model computational complexity problem by introducing for the first time an object-oriented target scattering simulation system.
It is a purpose of this invention to provide a new implementation of a detailed sonar target scattering model made possible for the first time by using object-oriented techniques to implement the broadband computational simulation of a plurality of detailed target highlight features. It is a feature of this invention that the class library includes a new target class and a new highlight base class from which a plurality of highlight subclasses are drawn to represent a wide range of target highlight features. It is an advantage of this invention that the resulting standard high-level framework allows many operations to be naturally defined and used with reduced software code errors, thereby improving computational effectiveness.
In one aspect, the invention is a machine-implemented method of simulating an acoustic received signal arising from an acoustic source signal scattered by a target having a plurality of highlights, the method comprising the unordered steps of storing in a data memory information representing the properties of the acoustic source signal, storing in the data memory information representing medium properties selected from the group that includes velocity, density, and scattering properties, storing in the data memory information representing the geometric relationship of the simulated positions of an acoustic source, an acoustic receiver, and the target, storing in the data memory a class library including a target class having a plurality of methods, a highlight base class and one or more highlight subclasses each having a plurality of methods, instantiating from the stored class library a target object representing the target, instantiating from the stored class library a highlight object representing one or more of the target highlights, executing a plurality of the methods in the target and highlight objects to predict the simulated acoustic received signal, and displaying the simulated acoustic received signal.
In a preferred embodiment, the invention is a system for simulating an acoustic received signal arising from an acoustic source signal scattered by a target having a plurality of highlights, the system comprising a data processor; a user interface coupled to the data processor for accepting user commands and data; a data memory coupled to the data processor for storing information and executable processor instructions, including information representing the properties of the acoustic source signal, information representing medium propagation properties selected from the group that includes velocity, density, and scattering properties, information representing the geometric relationship of the simulated positions of an acoustic source, an acoustic receiver, and the target, a class library including a target class having a plurality of methods, a highlight base class and one or more highlight subclasses each having a plurality of methods, program means for instantiating from the stored class library a target object representing the target, program means for instantiating from the stored class library a highlight object representing one or more of the target highlights, and program means for executing a plurality of the methods in the target and highlight objects to predict the simulated acoustic received signal; and a display coupled to the data processor for displaying the simulated acoustic received signal.
In yet another aspect, the invention is a computer program product for use with a system for simulating an acoustic received signal arising from an acoustic source signal scattered by a target having a plurality of highlights, the system including a data memory and a display device, the computer program product including a recording medium on which are recorded program means for directing the system to store in the data memory information representing the properties of the acoustic source signal, program means for directing the system to store in the data memory information representing medium properties selected from the group that includes velocity, density, and scattering properties, program means for directing the system to store in the data memory information representing the geometric relationship of the simulated positions of an acoustic source, an acoustic receiver, and the target, program means for directing the system to store in the data memory a class library including a target class having a plurality of methods, a highlight base class and one or more highlight subclasses each having a plurality of methods, program means for directing the system to instantiate from the stored class library a target object representing the target, program means for directing the system to instantiate from the stored class library a highlight object representing one or more of the target highlights, program means for directing the system to execute a plurality of the methods in the target and highlight objects to predict the simulated acoustic received signal, and program means for directing the system to display on the display device the simulated acoustic received signal.
The foregoing, together with other objects, features and advantages of this invention, can be better appreciated with reference to the following specification, claims and the accompanying drawing.